Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$143.60	4.793%	$150.4827	$150.48	$150.50	$150.50
Purchase #2	$160.41	9.425%	$175.5286	$175.53	$175.55	$175.50
Purchase #3	$78.53	5.594%	$82.923	$82.92	$82.90	$82.90
Purchase #4	$52.95	3.372%	$54.7355	$54.74	$54.75	$54.70
Purchase #5	$171.36	12.199%	$192.2642	$192.26	$192.25	$192.30
Purchase #6	$124.39	6.386%	$132.3335	$132.33	$132.35	$132.30
Purchase #7	$138.26	8.572%	$150.1116	$150.11	$150.10	$150.10
7 purchase totals =	$869.50		$938.3791	$938.37	$938.40	$938.30